Power converters are used to convert an electrical input power to an output power and are for example frequently used in power supplies to generate a voltage and/or current for a certain appliance based on an externally supplied power, for example a mains power. Power converters may for example be voltage converters converting an input voltage to one or more output voltages, which may be regulated to one or more predefined voltage levels.
Voltage controllers include AC/DC (alternating current/direct current) converters, DC/DC converters or DC/AC converters. One class of such voltage converters includes switched mode power supplies (SMPS). An SMPS uses controlled charging and discharging of an inductor or transformer by operating one or more switches which a switching frequency and is an efficient way to convert power. Examples for SMPS include buck converters, boost converters, flyback converters or resonant converters like LLC (inductor-inductor-capacitor) converters.
In some applications, power converters are required to support operation under various load conditions, ranging from a high load to a light load where very little or no power is required. For example, in lighting applications like power supplies for light emitting diode (LED) arrangements light sources like LEDs may be made dimmable. In such cases, the light output may be essentially continuously regulated between a full light output (brightest operation) to no light output (switched-off state, dark). In such applications, the required output power may vary between a full output power and zero continuously.
To provide a required output power, for example output voltage, conventionally a feedback loop is used which provides an indication of the output to a controller of the power supply. This ensures that for example the voltage for a light source arrangement like an LED arrangement is stable under all load conditions and corresponds to a voltage required by the light source arrangement.
In some applications, besides a variable load like a light source arrangement, other loads have to be supplied by the power supply, such as sensors or communication devices for example for Bluetooth communication, ZigBee communication or Wi-Fi communication. A straight forward way to provide power to such other loads is to provide a plurality of power supplies. However, this is a costly solution, and therefore it may be desirable to supply various loads with a single power supply. One way to do this is using a power converter type which supports a plurality of outputs, for example a flyback converter with a plurality of secondary windings. The turns ratio of the respective windings determines a voltage ratio between the different outputs and an input voltage. For ease of explanation, an output of the power converter to which a main load (for example light source arrangement) is connected will be referred to as main output, whereas an output to which other loads are connected will be referred to as auxiliary output herein.
In some implementations, only the main output is regulated based on a feedback signal as discussed above. In such a case, when the load coupled to the main output drops, for example when a light source arrangement is turned off, the main output requests only minimal power. If a load on the auxiliary output is high during this time, the average voltage provided on the auxiliary output may drop too low, and ripples of the auxiliary output voltage may become high, which is undesirable.
Besides providing a separate power supply, a conventional approach to remedy this problem is the use of a plurality of feedback signals, one from each output and combining the feedbacks to a single feedback signal, which is then used for regulation. While this may in some implementations ensure a good regulation of all regulated outputs, the system optimization to combine both feedback signals is complicated to provide a stable overall regulation. Moreover, it may be difficult to provide an isolation (galvanic separation between output side and input side of the power supply) for all feedback signals, and the number of components needed to implement such a solution may be high, which increases costs. Also other conventional solutions may have their drawbacks.